No play for Hayne as 49ers lose

Jarryd Hayne says his demotion to the bench for the San Francisco 49ers' biggest game of the year only motivates him to get better.

Hayne had to watch from the sidelines as arch rivals the Seattle Seahawks thumped the 49ers 20-3 on their home field, Levi's Stadium, on Thursday.

The former NRL star was replaced by veteran running back and punt returner Reggie Bush.

"I enjoy challenges," Hayne told reporters after the game.

"Obviously one of those is to be active again."

Hayne had played in all four pre-season and six regular season games with mixed results.

There were flashes of brilliance, highlight reel catches and slashing runs, but he also had three fumbles and last weekend as a running back against the Baltimore Ravens failed to protect quarterback Colin Kaepernick from being sacked.

His coach Jim Tomsula broke the news to Hayne that he was not in the 46-man squad for the Seahawks.

"He didn't like it, but he was fine," Tomsula said.

Hayne said he asked Tomsula what he needed to do to get better, but the Australian declined to tell reporters what the coach said.

With Bush returning from a calf injury and the 49ers' top running back Carlos Hyde playing with a foot injury, Tomsula had the choice of playing rookie Mike Davis or Hayne as the third back-up.

Davis got the job, but did not have a single rushing attempt against the Seahawks.

Bush had 21 yards from four carries, while Hyde battled with 11 carries for 40 yards.

Whereas Hayne took risks as a punt returner, Bush was conservative against the Seahawks.

Bush let two punts bounce, called a fair catch on another and on his only return took the ball back nine yards.

A win was crucial for the 49ers and Seahawks, with both teams entering the game with two win, four loss records.

The loss may have extinguished the 49ers' hopes of a playoff spot and leaves them languishing in last place in the NFL's NFC West division.

Hayne turned his back on millions of dollars in the NRL to test his chances in the NFL and he knew it would not be an easy road.

"It's a cut-throat sport," Hayne said.

"I know that. We all know that.

"... I'm just going to embrace it and keep working hard and move forward."

Seahawks quarterback Russell Wilson took command of the game with 18 completed passes from 24 attempts for 235 yards, one touchdown and two interceptions.